Static METAR Plots

These are a set of static plots generated by ADDS showing a composite
station model plot (see Station Format below) for a set of stations in a
particular region. There are 19 regions plus a CONUS view. Each plot is
updated every 5 minutes. The web page we refresh every 15 minutes.

Station Model Format

The station model plot is a standardized way of showing muliple pieces
of data at a partcular site. Some of the data are coded and others are shown
as symbols. Fig. 1 shows the layout of data. The parameters are:

Figure 1: Surface Station Data Format

Temp - Temperature plotted in the upper left in Fahrenheit

Windbarb - The wind barb. The stick points in the direction the
winds are coming from. Each full barb represents 10 knots of wind. Each
half barb represents 5 knots. In this case, you have winds from the NNW at
15 knots. If there are wind gusts, the number will be displayed at the end
of the barb as G23 or gusts to 23 knots.

Alt - Last three digits of the altimeter setting plotted upper
right in inches Hg. In this case, 032 represents 30.32 inches Hg.

Id - The last 3 letters of the ICAO identifier for the site. LWV
is Lawrenceville IL.

Dew - The dewpoint temperature plotted in the lower left in F.

Vis - The visibility plotted to the left of the weather symbol,
in statute miles.

Wx - A symbol representing present weather plotted just to the left
of the cloud cover symbol.

Cover - The cloud cover symbol is plotted in the center. The amount
the circle is filled represents the amount of cloud cover. In this case, it's
overcast. The color of the circle represents the flight conditions:

green - VFR (Visual Flight Rules)

blue - MVFR (Marginal Visual Flight Rules)

red - IFR (Instrument Flight Rules)

purple - LIFR (Low Instrument Flight Rules)

Wind barbs

The wind barbs types are shown in Fig. 2. Calm winds are shown as a
concentric around the station location. Long barbs are 10 knots. Short barbs
are 5 knots. A flag represents 50 knots. Five knots is a short barb offset
from the end. The barb always points in the direction the winds are coming
from.

Figure 2: Wind Barb Sample

Flight category definitions

Category

Color

Ceiling

Visibility

LIFR
Low Instrument Flight Rules

Magenta

below 500 feet AGL

and-or

less than 1 mile

IFR
Instrument Flight Rules

Red

500 to below 1,000 feet AGL

and/or

1 mile to less than 3 miles

MVFR
Marginal Visual Flight Rules

Blue

1,000 to 3,000 feet AGL

and/or

3 to 5 miles

VFR
Visual Flight Rules

Green

greater than 3,000 feet AGL

and

greater than 5 miles

NOTES:By definition, IFR is ceiling less
than 1,000 feet AGL and/or visibility less
than 3 miles while LIFR is a sub-category of IFR.
By definition, VFR is ceiling greater than or equal
to 3,000 feet AGL and visibility greater than or equal to
5 miles while MVFR is a sub-category of VFR.

Cloud coverage symbols

Figure 3: Cloud Clover Symbols

Automated stations report "CLR" when clouds may exist above
12,000 feet so a square is used to represent this uncertainty whereas
an unfilled circle is used for "SKC" which a human reports the
sky is completely clear overhead. The abbreviation "OVX" is
unofficial but ADDS uses it here to indicate the sky is obscured which
is the case when a METAR reports vertical visibility and no cloud
information.

Present Weather symbols

Figure 4: Present Weather Symbols

Plots of station data may include one of
the following symbols to represent the present weather. METARs may
include more than one type of weather condition but only one icon ever
gets plotted. Two additional documents show the original descriptions
abridged from the World Meteorological Organization (WMO) and which
symbol is plotted for each present weather text string. These are not
necessarily official but they represent our best matching of weather
conditions to the original WMO table of icons.